[Study of membrane-bound ribosomes during pea chloroplasts formation]

Membrane-bound ribosomes of chloroplasts, isolated from pea seedlings during grana formation, can be partially liberated by 0.5 M KCl and 0.001 M puromycin. In case of mature chloroplasts, after the completion of grana formation process these agents are inefficient, and liberation of ribosomes and polyribosomes may be achieved only after solubilization of thylakoid membranes by 1% Triton X-100. Electron microscopic study of the heavy membrane fraction of young chloroplasts reveals electron-transparent membranes, containing rings and discs of thylakoids with a diameter of about 2 mum. These rings are liberated together with ribosomes under the action of 0.5 M KCl; Triton X-100 liberates equally-sized annular polyribosomes. The rings detected in chloroplast membranes at early stages of development are regarded as structures, precursor grana thylakoids, and the annular polyribosomes included into them as immediate participants of thylakoid morphogenesis.